Metering is involved in many application domains such as electricity metering, water metering, gas metering, pay as you drive car insurance, traffic congestion charging, on-line services metering such as pay-per-view digital rights management, software as a service metering and others. However, as the sophistication of the metering increases there are concerns about user privacy protection. For example, it may be possible, through fine grain electricity meter readings, to identify which electrical appliances are used through load monitoring. Detailed consumption data may facilitate the creation of users' lifestyle profiles, with information such as when they are at home, when they eat, whether they arrive late to work and so on. User privacy concerns arise where there is metering in other application domains. For example, pay-as-you drive car insurance, tolling or taxation based on the time, distance and location of a vehicle may potentially make that fine grained information available to providers.
Existing approaches for protecting user privacy where metering is carried out are typically administrative, for example, being based on codes of conduct, regulations and legislation.
Other solutions for protecting users' privacy have involved enabling groups of users living in the same neighborhood to compute the sum of their consumption without disclosing their individual consumption. However this type of approach is complex and relies on collaboration between users in the group. The embodiments described below are not limited to implementations which solve any or all of the disadvantages of known privacy-preserving metering systems.